92 f150 5.0 2wd XLT

Past while now after driving the truck for 10mins+ and shutting down an attempting to restart I have to put the battery start aid on it to start it. When trying to start it, inside the cab indicates im getting around 8v when trying to start. When I connect my voltmeter to it and attempt to start it with a no load around 14v and a start load around 8v it makes me wonder. Battery is 3yrs old.

One day I had this happen at walmart and a walmart mechanic came out to test the battery. The battery tester while the battery was still in the truck indicated that I had a power leak from somewhere.
- Black cable from battery to front of block was secure.
- Black cable from top left of block to firewall seemed secure
- Black cable from battery to side of engine bay seemed secure
- Red cable from battery to starter selenoid seemed secure w/ no frays
- Red cable from battery to starter seemed secure w/ no frays
- Red cable from selenoid to starter seemed secure

Ive read this and understood it. However I can't get past step #1 of testing the battery drop under load due to a drop of nearly 5v. But also concerns me of the mechanic not being able to test it while its in the truck with the key off due to the machine picking up a voltage leak.... Any ideas????
https://www.ford-trucks.com/forums/1...ow-starter.htm

 

Also on a side note when the truck is running my gauge reads just fine..... about 60% of the interior gauge path. When I also shut down the truck after driving I still have a good voltage.

 

If the battery drops to 8V during start it's time for a new battery most likely.

9.6V is basically the limit. There are temperature allowances when it gets cold, or it may be the battery simply needs charging, but you'll have a better idea on that stuff.

 

Even after I charge it and try to start I get a drop from 13+v down to 8v- within seconds.

 

I would recommend determining the source of the parasitic aka "phantom load". Otherwise it will just ruin the next battery you buy. And then the alternator will start complaining shortly after that and may decide to go on strike. They aren't really designed to re-charge dead or nearly dead batts. Could be a stuck relay causing the drain, maybe an aftermarket stereo or other accessory wigging out etc. Typically about 50 milliamperes total current draw at "rest" is considered OK, maybe a little more, in a vehicle after 1 hour. That's less than a tenth of an amp.

Put the ammeter in series with a cable terminal and battery post. Modern cars and trucks have all kinds of boxes and gee-gaws and computer modules, security system etc that spool up and do their thing for up to an hour after shutdown. During that time maybe up to 4 or 5 amps draw isn't unusual. Hook everything up. Wait at least an hour for everything to go to "sleep." Be careful, if you open a door or turn the key on that might wake a module up. Anyway see what the "at rest" current draw is. If it exceeds 50 mA or so, you'll have to do some 'vestigatin'. Start pulling fuses to divide and isolate systems and try to narrow it down.

 

That doesn't mean too much. Some ... but not a whole lot. A battery will very often measure 12+ volts across the terminals or open circuit, but as soon as any kind of real load is applied it chokes. Just like it's doing when you go to start. That's a "load test". Remember too a battery to be considered good has to be able to hold a charge, not just charge.

What happens when you turn on the headlights? How about when cranking the engine with headlights on, do they stay bright, dim a little, or dim a lot?

 

Any progress? Let us know what you find.